server crash with client switch

[totaam]

Was testing #3439, so the server is Ubuntu 20.04.
The bug only occurs if I first connect with a dual 4K Fedora client, then with a much smaller MS Windows client.

Traceback (most recent call first):
  File "/usr/lib/python3/dist-packages/xpra/x11/models/window.py", line 498, in _do_update_client_geometry
    self.corral_window.move_resize(x, y, w, h)
  File "/usr/lib/python3/dist-packages/xpra/x11/models/window.py", line 487, in _update_client_geometry
    self._do_update_client_geometry(window_size, window_position)
  File "/usr/lib/python3/dist-packages/xpra/x11/models/window.py", line 1275, in _handle_wm_normal_hints_change
  File "/usr/lib/python3/dist-packages/xpra/x11/models/core.py", line 565, in _handle_property_change
    handler(self)
  File "/usr/lib/python3/dist-packages/xpra/x11/models/core.py", line 531, in do_xpra_property_notify_event
    self._handle_property_change(str(event.atom))
  File "/usr/lib/python3/dist-packages/xpra/x11/models/window.py", line 395, in do_xpra_property_notify_event
    super().do_xpra_property_notify_event(event)
  <built-in method emit of WindowModel object at remote 0x7fffaf949e40>
  File "/usr/lib/python3/dist-packages/gi/overrides/Gtk.py", line 1632, in main
    return _Gtk_main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/xpra/server/gtk_server_base.py", line 119, in do_run
--Type <RET> for more, q to quit, c to continue without paging--
    Gtk.main()
  File "/usr/lib/python3/dist-packages/xpra/server/server_core.py", line 434, in run
    self.do_run()
  File "/usr/lib/python3/dist-packages/xpra/scripts/server.py", line 4450, in _do_run_server
  File "/usr/lib/python3/dist-packages/xpra/scripts/server.py", line 924, in do_run_server
    if xrd=="/run/user/%i" % uid:
  File "/usr/lib/python3/dist-packages/xpra/scripts/main.py", line 4071, in run_server
  File "/usr/lib/python3/dist-packages/xpra/scripts/main.py", line 458, in do_run_mode
    return run_server(script_file, cmdline, error_cb, options, args, mode, defaults)
  File "/usr/lib/python3/dist-packages/xpra/scripts/main.py", line 680, in run_mode
    d = {}
  File "/usr/lib/python3/dist-packages/xpra/scripts/main.py", line 142, in main
    return run_mode(script_file, cmdline, err, options, args, mode, defaults)
  File "/usr/bin/xpra", line 10, in <module>
    sys.exit(main(sys.argv[0], sys.argv))

#0  0x00007ffff4d588b5 in ?? () from /lib/x86_64-linux-gnu/libgdk-3.so.0
#1  0x00007ffff4d59389 in ?? () from /lib/x86_64-linux-gnu/libgdk-3.so.0
#2  0x00007ffff4d33467 in ?? () from /lib/x86_64-linux-gnu/libgdk-3.so.0
#3  0x00007ffff6798ff5 in ?? () from /lib/x86_64-linux-gnu/libffi.so.7
#4  0x00007ffff679840a in ?? () from /lib/x86_64-linux-gnu/libffi.so.7
#5  0x00007ffff69880a5 in ?? ()
   from /usr/lib/python3/dist-packages/gi/_gi.cpython-38-x86_64-linux-gnu.so
#6  0x00007ffff697f25c in ?? ()
   from /usr/lib/python3/dist-packages/gi/_gi.cpython-38-x86_64-linux-gnu.so
#7  0x00007ffff698319d in ?? ()
   from /usr/lib/python3/dist-packages/gi/_gi.cpython-38-x86_64-linux-gnu.so
#8  0x00000000005f3e1e in _PyObject_MakeTpCall (
    callable=<gi.FunctionInfo at remote 0x7fffc3f84fb0>, args=<optimized out>, 
    nargs=<optimized out>, keywords=<optimized out>)
    at ../Include/internal/pycore_pyerrors.h:13
#9  0x0000000000570674 in _PyObject_Vectorcall (kwnames=0x0, 
    nargsf=<optimized out>, args=0x150afd8, 
    callable=<gi.FunctionInfo at remote 0x7fffc3f84fb0>)
    at ../Include/cpython/abstract.h:125
#10 _PyObject_Vectorcall (kwnames=0x0, nargsf=<optimized out>, args=0x150afd8, 
    callable=<gi.FunctionInfo at remote 0x7fffc3f84fb0>)
    at ../Include/cpython/abstract.h:115
#11 call_function (kwnames=0x0, oparg=<optimized out>, 
--Type <RET> for more, q to quit, c to continue without paging--
    pp_stack=<synthetic pointer>, tstate=0x9634f0) at ../Python/ceval.c:4963
#12 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>)
    at ../Python/ceval.c:3469
#13 0x00000000005f6836 in PyEval_EvalFrameEx (throwflag=0, 
    f=Frame 0x150ae10, for file /usr/lib/python3/dist-packages/xpra/x11/models/window.py, line 498, in _do_update_client_geometry (self=<WindowModel(_gproperties={'client-window': <X11Window(_xpra_window_event_receivers={<...>, <CompositeHelper(client_window=<...>, xid=16777222, _use_xshm=True, _damage_handle=4194339, _xshm_handle=<xpra.x11.bindings.ximage.XShmWrapper at remote 0x7fffaf7b70b0>, _contents_handle=<xpra.x11.bindings.ximage.PixmapWrapper at remote 0x7fffb60368d0>, _border_width=0, _listening_to=[<X11Window(_xpra_window_event_receivers={<...>, <...>}) at remote 0x7fffaf7b9740>]) at remote 0x7fffaf94dc80>}) at remote 0x7fffaf949e00>, 'geometry': (182, 167, 894, 582), 'decorations': -1, 'state': frozenset(), 'depth': 32, 'xid': 16777222, 'pid': 9931, 'has-alpha': True, 'allowed-actions': ['_NET_WM_ACTION_CLOSE', '_NET_WM_ACTION_MOVE', '_NET_WM_ACTION_RESIZE', '_NET_WM_ACTION_FULLSCREEN', '_NET_WM_ACTION_MINIMIZE', '_NET_WM_ACTION_SHADE', '_NET_WM_ACTION_STICK', '_NET_WM_ACTION_MAXIMIZE_HORZ', '_NET_WM_ACT...(truncated)) at ../Python/ceval.c:741

[totaam]

Last messages from -d all:

2022-05-07 14:11:50,515 startup_complete()
2022-05-07 14:11:50,515 org.xpra.Server.Event(startup-complete, ['5a89bfb8332bc10ead38d9eda7ae04fc35e8d2682df02ba2b975bddf01ec21f0'])
2022-05-07 14:11:50,516 changed tcp socket to nodelay=False
2022-05-07 14:11:50,520 server-event: ('startup-complete', '5a89bfb8332bc10ead38d9eda7ae04fc35e8d2682df02ba2b975bddf01ec21f0')
2022-05-07 14:11:50,520 exec_on_connect_commands() start=[], start_child=[]
2022-05-07 14:11:50,521 x_event_filter event=('xpra-property-notify-event', None)/PropertyNotify window=0x400002
2022-05-07 14:11:50,521 parse_event(..)=<X11:PropertyNotify {'send_event': '0', 'serial': '0x1660', 'delivered_to': '0x400002', 'window': '0x400002', 'atom': '_XSETTINGS_SETTINGS', 'time': '8377186'}>
2022-05-07 14:11:50,521 x_event_filter event=('xpra-property-notify-event', None)/PropertyNotify took 0.6ms
2022-05-07 14:11:50,522 packet type send alias not found for 'stop'
2022-05-07 14:11:50,528 read thread: eof
2022-05-07 14:11:50,529 io_thread_loop(read, <bound method Protocol._read of Protocol(Pipe(audio capture))>) loop ended, closed=False
[Thread 0x7fffcdfbb700 (LWP 10464) exited]
2022-05-07 14:11:50,529 parse thread: empty marker, exiting
[Thread 0x7fffb6b8a700 (LWP 10511) exited]
2022-05-07 14:11:50,530 packet type send alias not found for 'exit'
2022-05-07 14:11:50,532 source_subprocess_wrapper(10462).stop_process() sending stop request to audio capture
2022-05-07 14:11:50,534 source_subprocess_wrapper(None).stop_protocol() calling <bound method Protocol.close of Protocol(Pipe(audio capture))>
2022-05-07 14:11:50,534 Protocol.close(None) closed=False, connection=Pipe(audio capture)
2022-05-07 14:11:50,534 Protocol.close(None) calling <bound method TwoFileConnection.close of Pipe(audio capture)>
2022-05-07 14:11:50,535 Pipe(audio capture).close() close callback=<bound method subprocess_caller.subprocess_exit of source_subprocess_wrapper(None)>, readable=<_io.BufferedReader name=48>, writeable=<_io.BufferedWriter name=47>
2022-05-07 14:11:50,538 Pipe(audio capture).close() calling <bound method subprocess_caller.subprocess_exit of source_subprocess_wrapper(None)>
2022-05-07 14:11:50,539 subprocess_exit() command=['python3.8', '/usr/bin/xpra', '--windows=no', '--video-encoders=none', '--csc-modules=none', '--video-decoders=none', '--proxy-video-encoders=none', '_sound_record', '-', '-', 'pulsesrc', 'device=Xpra-Speaker.monitor', 'opus', '', '1.0']
2022-05-07 14:11:50,539 firing callback for 'exit': [(<bound method AudioMixin.sound_source_exit of ClientConnectionMuxer(1 : None)>, [])]
[New Thread 0x7fffb6b8a700 (LWP 10625)]
2022-05-07 14:11:50,540 close_files_thread() _readable=<_io.BufferedReader name=48>
2022-05-07 14:11:50,541 Pipe(audio capture).close() done
2022-05-07 14:11:50,566 terminate_queue_threads()
[Thread 0x7fffb764c700 (LWP 10612) exited]
2022-05-07 14:11:50,567 write thread: empty marker, exiting
2022-05-07 14:11:50,568 Protocol.close(None) closed=True, connection=None
2022-05-07 14:11:50,568 io_thread_loop(write, <bound method Protocol._write of Protocol(None)>) loop ended, closed=True
[Thread 0x7ffff0b9b700 (LWP 10613) exited]
2022-05-07 14:11:50,570 Protocol.close(None) done
[New Thread 0x7ffff0b9b700 (LWP 10626)]
2022-05-07 14:11:50,545 close_files_thread() calling <built-in method close of _io.BufferedReader object at 0x7ffff274df60>
2022-05-07 14:11:50,574 close_files_thread() _writeable=<_io.BufferedWriter name=47>
2022-05-07 14:11:50,574 close_files_thread() calling <built-in method close of _io.BufferedWriter object at 0x7fffd821b510>
[Thread 0x7fffb6b8a700 (LWP 10625) exited]
2022-05-07 14:11:50,576 compress_and_send_window_icon() 64x64 in RGBA format, 16384 bytes for wid=1
2022-05-07 14:11:50,577 get_cursor_image() cursor=[1665, 1223, 16, 16, 7, 7, 1, '1024 bytes', b'']
2022-05-07 14:11:50,587 get_cursor_data(): default cursor - clearing it
2022-05-07 14:11:50,587 send_empty_cursor(..)
2022-05-07 14:11:50,589 x_event_filter event=('xpra-property-notify-event', None)/PropertyNotify window=0x1400006
2022-05-07 14:11:50,584 compress_and_send_window_icon: 64x64 (max-size=(128, 128), standard-size=(64, 64)), pixel_format=RGBA
2022-05-07 14:11:50,594  must convert=True, must scale=False
2022-05-07 14:11:50,596 queuing window icon update: ('window-icon', 1, 64, 64, 'png', Compressed(png: 3346 bytes))
2022-05-07 14:11:50,597 parse_event(..)=<X11:PropertyNotify {'send_event': '0', 'serial': '0x1670', 'delivered_to': '0x1400006', 'window': '0x1400006', 'atom': 'WM_NORMAL_HINTS', 'time': '8377216'}>
2022-05-07 14:11:50,597 changed tcp socket to cork=True
2022-05-07 14:11:50,602 changed tcp socket to cork=False
2022-05-07 14:11:50,603 Property changed on 0x1400006: WM_NORMAL_HINTS
2022-05-07 14:11:50,603 WM_NORMAL_HINTS={'min_size': (327, 72), 'base_size': (14, 33), 'resize_inc': (11, 23), 'win_gravity': 1}
2022-05-07 14:11:50,604 get(decorations, -1) using get_property=-1
2022-05-07 14:11:50,604 updateprop(size-hints, {'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)}) previous value={'base-size': (14, 28), 'increment': (9, 18), 'gravity': 1, 'minimum-size': (327, 72)}
2022-05-07 14:11:50,604 updating metadata on WindowModel(0x1400006): <GParamBoxed 'size-hints'>
2022-05-07 14:11:50,604 can_send_window(WindowModel(0x1400006))=True
2022-05-07 14:11:50,605 make_metadata(2, WindowModel(0x1400006), size-hints)={'size-constraints': {'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)}}
2022-05-07 14:11:50,605 changed tcp socket to nodelay=True
2022-05-07 14:11:50,606 updated: size-hints={'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)}
2022-05-07 14:11:50,606 _update_client_geometry: ignored, owner=None, setup_done=True
2022-05-07 14:11:50,606 _do_update_client_geometry: allocated 734x460 (from <function WindowModel._update_client_geometry.<locals>.window_size at 0x7fffb5fc2940>)
2022-05-07 14:11:50,606 calc_constrained_size(734, 460, typedict({'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)}))=(729, 447) (size_constraints=(166, 47, 32767, 32767))
2022-05-07 14:11:50,606 _do_update_client_geometry: size({'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)})=729x447
2022-05-07 14:11:50,606 _do_update_client_geometry: position=3922x114 (from <function WindowModel._update_client_geometry.<locals>.window_position at 0x7fffb5fc29d0>)
2022-05-07 14:11:50,597 compress_and_send_window_icon() 48x48 in BGRA format, 9216 bytes for wid=2
2022-05-07 14:11:50,627 compress_and_send_window_icon: 48x48 (max-size=(128, 128), standard-size=(64, 64)), pixel_format=BGRA
2022-05-07 14:11:50,628  must convert=True, must scale=False
2022-05-07 14:11:50,629 queuing window icon update: ('window-icon', 2, 48, 48, 'png', Compressed(png: 1193 bytes))
2022-05-07 14:11:50,638 changed tcp socket to nodelay=False
2022-05-07 14:11:50,638 changed tcp socket to cork=True
2022-05-07 14:11:50,638 changed tcp socket to cork=False

Summary:

• startup_complete() and associated dbus event
• XSettings update
• audio stop / exit for previous connection, close_files_thread etc
• send_empty_cursor
• update to WM_NORMAL_HINTS={'min_size': (327, 72), 'base_size': (14, 33), 'resize_inc': (11, 23), 'win_gravity': 1}
• updated: size-hints={'base-size': (14, 33), 'increment': (11, 23), 'gravity': 1, 'minimum-size': (327, 72)}
• _do_update_client_geometry: position=3922x114 (from <function WindowModel._update_client_geometry.<locals>.window_position at 0x7fffb5fc29d0>)
• compress_and_send_window_icon

Suspicions: possibly the audio subprocess exit and one of its callbacks.
More likely: the update-client-geometry calls.

Reproducible with Fedora 4.4 latest server.

[totaam]

With XPRA_WINDOW_PROPERTIES_DEBUG="size-hints":

2022-05-07 15:59:32,576 updateprop(size-hints, {'base-size': (16, 31), 'increment': (11, 26), 'gravity': 1, 'minimum-size': (371, 80)}) previous value={'base-size': (16, 31), 'increment': (11, 26), 'gravity': 1, 'minimum-size': (317, 75)}

The minimum size has changed from (317, 75) to (371, 80).
Why gnome-terminal does this isn't clear, perhaps due to some XSettings or DPI value change.
In any case, we end up calling _do_update_client_geometry and this should never crash.
Commenting out self.corral_window.move_resize(x, y, w, h) "fixes" things, except the window is no longer visible since it remains mapped where it was before, which is now outside the new client's desktop area.

[totaam]

I couldn't figure it out because the ownership-election logic was just far too complicated for my brain.
So in the end, I removed it in an attempt to understand what was really going on... and that fixed things?!

The new problems are:

• what to backport? (as this is too big a change to backport)
• should the DesktopManager also be removed? (probably)